Introduce the constrained network server.

media/tools/constrained_network_server/cns.py

Index: media/tools/constrained_network_server/cns.py
diff --git a/media/tools/constrained_network_server/cns.py b/media/tools/constrained_network_server/cns.py
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+#!/usr/bin/python
+
+# Copyright (c) 2011 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""Constrained Network Server. Serves files with supplied network constraints.
+
+The CNS exposes a web based API allowing network constraints to be imposed on
+file serving.
+
+TODO(dalecurtis): Add some more docs here.
+
+"""
+
+import optparse
+import os
+import signal
+import sys
+import threading
+import time
+
+try:
+  import cherrypy
+except ImportError:
+  print ('CNS requires CherryPy v3 or higher to be installed. Please install\n'
+         'and try again. On Linux: sudo apt-get install python-cherrypy3\n')
+  sys.exit(1)
+
+
+# Default port to serve the CNS on.
+_DEFAULT_SERVING_PORT = 80
+
+# Default port range for constrained use.
+_DEFAULT_CNS_PORT_RANGE = (50000, 51000)
+
+# Default number of seconds before a port can be torn down.
+_DEFAULT_PORT_EXPIRY_TIME_SECS = 5 * 60
+
+
+class PortAllocator(object):
+  """Dynamically allocates/deallocates ports with a given set of constraints."""
+
+  def __init__(self, port_range, expiry_time_secs=5 * 60):
+    """Sets up initial state for the Port Allocator.
+
+    Args:
+      port_range: Range of ports available for allocation.
+      expiry_time_secs: Amount of time in seconds before constrained ports are
+          cleaned up.
+    """
+    self._port_range = port_range
+    self._expiry_time_secs = expiry_time_secs
+
+    # Keeps track of ports we've used, the creation key, and the last request
+    # time for the port so they can be cached and cleaned up later.
+    self._ports = {}
+
+    # Locks port creation and cleanup. TODO(dalecurtis): If performance becomes
+    # an issue a per-port based lock system can be used instead.
+    self._port_lock = threading.Lock()
+
+  def Get(self, key, **kwargs):
+    """Sets up a constrained port using the requested parameters.
+
+    Requests for the same key and constraints will result in a cached port being
+    returned if possible.
+
+    Args:
+      key: Used to cache ports with the given constraints.
+      **kwargs: Constraints to pass into ***TODO*** ConstraintGenerator...
+
+    Returns:
+      None if no port can be setup or the port number of the constrained port.
+    """
+    with self._port_lock:
+      # Check port key cache to see if this port is already setup. Update the
+      # cache time and return the port if so. Performance isn't a concern here,
+      # so just iterate over ports dict for simplicity.
+      full_key = (key,) + tuple(kwargs.values())
+      for port, status in self._ports.iteritems():
+        if full_key == status['key']:
+          self._ports[port]['last_update'] = time.time()
+          return port
+
+      # Cleanup ports on new port requests. Do it after the cache check though
+      # so we don't erase and then setup the same port.
+      self._CleanupLocked(all_ports=False)
+
+      # Performance isn't really an issue here, so just iterate over the port
+      # range to find an unused port. If no port is found, None is returned.
+      for port in xrange(self._port_range[0], self._port_range[1]):
+        if port in self._ports:
+          continue
+
+        # TODO(dalecurtis): Integrate with shadi's scripts.
+        # We've found an open port so call the script and set it up.
+        #Port.Setup(port=port, **kwargs)
+
+        self._ports[port] = {'last_update': time.time(), 'key': full_key}
+        return port
+
+  def _CleanupLocked(self, all_ports):
+    """Internal cleanup method, expects lock to have already been acquired.
+
+    See Cleanup() for more information.
+
+    Args:
+      all_ports: Should all ports be torn down regardless of expiration?
+    """
+    now = time.time()
+    # Use .items() instead of .iteritems() so we can delete keys w/o error.
+    for port, status in self._ports.items():
+      expired = now - status['last_update'] > self._expiry_time_secs
+      if all_ports or expired:
+        cherrypy.log('Cleaning up port %d' % port)
+
+        # TODO(dalecurtis): Integrate with shadi's scripts.
+        #Port.Delete(port=port)
+
+        del self._ports[port]
+
+  def Cleanup(self, all_ports=False):
+    """Cleans up expired ports, or if all_ports=True, all allocated ports.
+
+    By default, ports which haven't been used for self._expiry_time_secs are
+    torn down. If all_ports=True then they are torn down regardless.
+
+    Args:
+      all_ports: Should all ports be torn down regardless of expiration?
+    """
+    with self._port_lock:
+      self._CleanupLocked(all_ports)
+
+
+class ConstrainedNetworkServer(object):
+  """A CherryPy-based HTTP server for serving files with network constraints."""
+
+  def __init__(self, options, port_allocator):
+    """Sets up initial state for the CNS.
+
+    Args:
+      options: optparse based class returned by ParseArgs()
+      port_allocator: A port allocator instance.
+    """
+    self._options = options
+    self._port_allocator = port_allocator
+
+  @cherrypy.expose
+  def ServeConstrained(self, f=None, bandwidth=None, latency=None, loss=None):
+    """Serves the requested file with the requested constraints.
+
+    Subsequent requests for the same constraints from the same IP will share the
+    previously created port. If no constraints are provided the file is served
+    as is.
+
+    Args:
+      f: path relative to http root of file to serve.
+      bandwidth: maximum allowed bandwidth for the provided port (integer
+          in kbit/s).
+      latency: time to add to each packet (integer in ms).
+      loss: percentage of packets to drop (integer, 0-100).
+    """
+    # CherryPy is a bit wonky at detecting parameters, so just make them all
+    # optional and validate them ourselves.
+    if not f:
+      raise cherrypy.HTTPError(400, 'Invalid request. File must be specified.')
+
+    # Sanitize and check the path to prevent www-root escapes.
+    sanitized_path = os.path.abspath(os.path.join(self._options.www_root, f))
+    if not sanitized_path.startswith(self._options.www_root):
+      raise cherrypy.HTTPError(403, 'Invalid file requested.')
+
+    # Check existence early to prevent wasted constraint setup.
+    if not os.path.exists(sanitized_path):
+      raise cherrypy.HTTPError(404, 'File not found.')
+
+    # If there are no constraints, just serve the file.
+    if bandwidth is None and latency is None and loss is None:
+      return cherrypy.lib.static.serve_file(sanitized_path)
+
+    # Validate inputs. isdigit() guarantees a natural number.
+    if bandwidth and not bandwidth.isdigit():
+      raise cherrypy.HTTPError(400, 'Invalid bandwidth constraint.')
+
+    if latency and not latency.isdigit():
+      raise cherrypy.HTTPError(400, 'Invalid latency constraint.')
+
+    if loss and not loss.isdigit() and not int(loss) <= 100:
+      raise cherrypy.HTTPError(400, 'Invalid loss constraint.')
+
+    # Allocate a port using the given constraints. If a port with the requested
+    # key is already allocated, it will be reused.
+    #
+    # TODO(dalecurtis): The key cherrypy.request.remote.ip might not be unique
+    # if build slaves are sharing the same VM.
+    constrained_port = self._port_allocator.Get(
+        cherrypy.request.remote.ip, bandwidth=bandwidth, latency=latency,
+        loss=loss)
+
+    if not constrained_port:
+      raise cherrypy.HTTPError(503, 'Service unavailable. Out of ports.')
+
+    # Build constrained URL. Only pass on the file parameter.
+    constrained_url = '%s?file=%s' % (
+        cherrypy.url().replace(
+            ':%d' % self._options.port, ':%d' % constrained_port),
+        f)
+
+    # Redirect request to the constrained port.
+    cherrypy.lib.cptools.redirect(constrained_url, internal=False)
+
+
+def ParseArgs():
+  """Define and parse the command-line arguments."""
+  parser = optparse.OptionParser()
+
+  parser.add_option('--expiry-time', type='int',
+                    default=_DEFAULT_PORT_EXPIRY_TIME_SECS,
+                    help=('Number of seconds before constrained ports expire'
+                          ' and are cleaned up. Default: %default'))
+  parser.add_option('--port', type='int', default=_DEFAULT_SERVING_PORT,
+                    help='Port to serve the API on. Default: %default')
+  parser.add_option('--port-range', default=_DEFAULT_CNS_PORT_RANGE,
+                    help=('Range of ports for constrained serving. Specify as'
+                          ' a comma separated value pair. Default: %default'))
+  parser.add_option('--eth', default='eth0',
+                    help=('Interface to setup constraints on. Use lo for a'
+                          ' local client. Default: %default'))
+  parser.add_option('--threads', type='int',
+                    default=cherrypy._cpserver.Server.thread_pool,
+                    help=('Number of threads in the thread pool. Default:'
+                          ' %default'))
+  parser.add_option('--www-root', default=os.getcwd(),
+                    help=('Directory root to serve files from. Defaults to the'
+                          ' current directory: %default'))
+
+  options = parser.parse_args()[0]
+
+  # Convert port range into the desired tuple format.
+  try:
+    if isinstance(options.port_range, str):
+      options.port_range = [int(port) for port in options.port_range.split(',')]
+  except ValueError:
+    parser.error('Invalid port range specified.')
+
+  # Normalize the path to remove any . or ..
+  options.www_root = os.path.normpath(options.www_root)
+
+  return options
+
+
+def Main():
+  """Configure and start the ConstrainedNetworkServer."""
+  options = ParseArgs()
+
+  cherrypy.config.update(
+      {'server.socket_host': '::', 'server.socket_port': options.port})
+
+  if options.threads:
+    cherrypy.config.update({'server.thread_pool': options.threads})
+
+  # Setup port allocator here so we can call cleanup on failures/exit.
+  pa = PortAllocator(options.port_range, expiry_time_secs=options.expiry_time)
+
+  try:
+    cherrypy.quickstart(ConstrainedNetworkServer(options, pa))
+  finally:
+    # Disable Ctrl-C handler to prevent interruption of cleanup.
+    signal.signal(signal.SIGINT, lambda signal, frame: None)
+    pa.Cleanup(all_ports=True)
+
+
+if __name__ == '__main__':
+  Main()